如何调整Mobile Vision扫描区域大小？SurfaceView调整失败求助

Hey there, I’ve been in your shoes before—trying to get a cropped scan area working instead of fullscreen can be tricky when the docs don’t spell it out clearly. Let’s break down some solutions that should work better than resizing SurfaceView directly:

CameraX is far more flexible than the legacy Camera APIs and is built to handle this kind of use case cleanly. Here’s how to set up a targeted scan region:

• First, add CameraX dependencies to your module-level build.gradle:

dependencies {
    def camerax_version = "1.3.0"
    implementation "androidx.camera:camera-core:$camerax_version"
    implementation "androidx.camera:camera-camera2:$camerax_version"
    implementation "androidx.camera:camera-lifecycle:$camerax_version"
    implementation "androidx.camera:camera-view:$camerax_version"
}

• Next, configure an ImageAnalysis use case with a custom crop rectangle to focus only on your desired scan area (e.g., a centered square):

val imageAnalysis = ImageAnalysis.Builder()
    .setTargetResolution(Size(1280, 720)) // Adjust to match your scanning needs
    .setBackpressureStrategy(ImageAnalysis.STRATEGY_KEEP_ONLY_LATEST)
    .build()

imageAnalysis.setAnalyzer(Executors.newSingleThreadExecutor()) { imageProxy ->
    // Define your crop region (example: centered 600x600 square)
    val cropRect = Rect(
        (imageProxy.width - 600)/2,
        (imageProxy.height - 600)/2,
        (imageProxy.width + 600)/2,
        (imageProxy.height + 600)/2
    )

    // Process only the cropped portion of the camera feed
    val croppedImage = imageProxy.image?.crop(cropRect)
    // Insert your scanning logic here using croppedImage

    imageProxy.close()
}

// Bind the use case to your activity/fragment lifecycle
CameraX.bindToLifecycle(this as LifecycleOwner, imageAnalysis)

• For the user-facing preview, overlay a custom guide view (like a centered rectangle outline) instead of resizing the preview itself. This keeps the camera feed clear while showing users exactly where to align their subject.

If you need to stick with SurfaceView, the core issue is usually aspect ratio mismatch causing distortion. Here’s how to fix it:

• Create a custom FrameLayout that enforces the camera preview’s aspect ratio (e.g., 16:9 or 4:3):

public class AspectRatioFrameLayout extends FrameLayout {
    private float mAspectRatio = 1.7777778f; // Default to 16:9

    public AspectRatioFrameLayout(Context context) {
        super(context);
    }

    public void setAspectRatio(float ratio) {
        mAspectRatio = ratio;
        requestLayout();
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        int width = MeasureSpec.getSize(widthMeasureSpec);
        int height = MeasureSpec.getSize(heightMeasureSpec);
        if (width == 0 || height == 0) return;

        float viewRatio = (float) width / height;
        float cameraRatio = mAspectRatio;

        // Adjust dimensions to match camera's aspect ratio
        if (viewRatio > cameraRatio) {
            width = (int) (height * cameraRatio);
        } else {
            height = (int) (width / cameraRatio);
        }

        setMeasuredDimension(width, height);
    }
}

• Wrap your SurfaceView in this custom layout, then set the aspect ratio to match your camera’s preview resolution. This ensures the preview doesn’t stretch or squish when you resize the SurfaceView to your desired scan area.

No matter which approach you use, a clear overlay helps users align their subject. Create a simple drawable for the overlay:

<!-- res/drawable/scan_overlay.xml -->
<shape xmlns:android="http://schemas.android.com/apk/res/android">
    <stroke android:width="2dp" android:color="#00FF00"/>
    <solid android:color="#80000000"/> <!-- Semi-transparent black outside the scan area -->
</shape>

Then add it to your layout over the camera preview:

<FrameLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <!-- Your Camera Preview (SurfaceView or CameraX PreviewView) -->
    <SurfaceView
        android:id="@+id/cameraPreview"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>

    <!-- Scan Region Overlay -->
    <View
        android:layout_width="600dp"
        android:layout_height="600dp"
        android:layout_gravity="center"
        android:background="@drawable/scan_overlay"/>
</FrameLayout>

内容的提问来源于stack exchange，提问作者Prost